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Boosting the thermal stability of emulsion–templated polymers via sulfonation: an efficient synthetic route to hierarchically porous carbon foams
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0001-5861-4281
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.ORCID iD: 0000-0003-2538-8104
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Structural Chemistry.
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2016 (English)In: ChemistrySelect, ISSN 2365-6549, Vol. 1, no 4, 784-792 p.Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

Hierarchically porous carbon foams with specific surface areas exceeding 600 m2 g−1 can be derived from polystyrene foams that are synthesized via water-in-oil emulsion templating. However, most styrene-based polymers lack strong crosslinks and are degraded to volatile products when heated above 400 oC. A common strategy employed to avert depolymerization is to introduce potential crosslinking sites such as sulfonic acids by sulfonating the polymers. This article unravels the thermal and chemical processes leading up to the conversion of sulfonated high internal phase emulsion polystyrenes (polyHIPEs) to sulfur containing carbon foams. During pyrolysis, the sulfonic acid groups (-SO3H) are transformed to sulfone (-C-SO2-C-) and then to thioether (-C−S-C-) crosslinks. These chemical transformations have been monitored using spectroscopic techniques: in situ IR, Raman, X-ray photoelectron and X-ray absorption near edge structure spectroscopy. Based on thermal analyses, the formation of thioether links is associated with increased thermal stability and thus a substantial decrease in volatilization of the polymers.

Place, publisher, year, edition, pages
2016. Vol. 1, no 4, 784-792 p.
Keyword [en]
Emulsion-templated polymer, sulfonation, pyrolysis, spectroscopy, carbon foam
National Category
Materials Chemistry
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-283174DOI: 10.1002/slct.201600139ISI: 000395395900026OAI: oai:DiVA.org:uu-283174DiVA: diva2:918694
Projects
3D microbatteries
Available from: 2016-04-11 Created: 2016-04-11 Last updated: 2017-10-30Bibliographically approved
In thesis
1. Multifunctional Carbon Foams by Emulsion Templating: Synthesis, Microstructure, and 3D Li-ion Microbatteries
Open this publication in new window or tab >>Multifunctional Carbon Foams by Emulsion Templating: Synthesis, Microstructure, and 3D Li-ion Microbatteries
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Carbon foams are among the existing electrode designs proposed for use in 3D Li-ion microbatteries. For such electrodes to find applications in practical microbatteries, however, their void sizes, specific surface areas and pore volumes need be optimized. This thesis concerns the synthesis of highly porous carbon foams and their multifunctional applications in 3D microbatteries. The carbon foams are derived from polymers that are obtained by polymerizing high internal phase water-in-oil emulsions (HIPEs).

In general, the carbonization of the sulfonated polymers yielded hierarchically porous structures with void sizes ranging from 2 to 35 µm and a BET specific surface area as high as 630 m2 g-1. Thermogravimetric and spectroscopic evidence indicated that the sulfonic acid groups, introduced during sulfonation, transformed above 250 oC to thioether (-C-S-) crosslinks which were responsible for the thermal stability and charring tendency of the polymer precursors. Depending on the preparation of the HIPEs, the specific surface areas and void-size distributions were observed to vary considerably. In addition, the pyrolysis temperature could also affect the microstructures, the degree of graphitization, and the surface chemistry of the carbon foams.

Various potential applications were explored for the bespoke carbon foams. First, their use as freestanding active materials in 3D microbatteries was studied. The carbon foams obtained at 700 to 1500 oC suffered from significant irreversible capacity loss during the initial discharge. In an effort to alleviate this drawback, the pyrolysis temperature was raised to 2200 oC. The resulting carbon foams were observed to deliver high, stable areal capacities over several cycles. Secondly, the possibility of using these structures as 3D current collectors for various active materials was investigated in-depth. As a proof-of-concept demonstration, positive active materials like polyaniline and LiFePO4 were deposited on the 3D architectures by means of electrodeposition and sol-gel approach, respectively. In both cases, the composite electrodes exhibited reasonably high cyclability and rate performance at different current densities. The syntheses of niobium and molybdenum oxides and their potential application as electrodes in microbatteries were also studied. In such applications, the carbon foams served dual purposes as 3D scaffolds and as reducing reactants in the carbothermal reduction process. Finally, a facile method of coating carbon substrates with oxide nanosheets was developed. The approach involved the exfoliation of crystalline VO2 to prepare dispersions of hydrated V2O5, which were subsequently cast onto CNT paper to form oxide films of different thicknesses.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 139 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1469
Keyword
Battery, Carbon, Electrochemical, Electrodeposition, Emulsion, Energy, Exfoliation, Foam, Lithium, Microbattery, Multifunctional, Nanoparticles, Polyaniline, Polymer, Power, Sol-gel, Storage, Structured, Three-dimensional
National Category
Materials Chemistry Composite Science and Engineering Polymer Technologies Inorganic Chemistry Physical Chemistry Polymer Chemistry Condensed Matter Physics
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-312897 (URN)978-91-554-9799-6 (ISBN)
Public defence
2017-03-03, Polhemsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2012–4681Swedish Energy Agency
Available from: 2017-02-08 Created: 2017-01-14 Last updated: 2017-02-15

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Asfaw, Habtom D.Younesi, RezaValvo, MarioMaibach, JuliaSahlberg, MartinNyholm, LeifEdström, Kristina

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